The present invention relates generally to load handling devices and more particularly concerns an improved swing drive assembly for large load handling cranes and the like.
It is known in the art, that the lifting capacity of a load handling drvice, can be increased by providing the device with a large diameter roller path for supporting on rollers an opposed boom and and a counterweight. One example of such a device is shown in U.S. Pat. No. 3,485,383. Such arrangements have afforded marked increases in the lifting capacities of the basic unit and have been quite satisfactory for many heavy duty lifting operations.
However, where the duty cycle for the device envolves both lifting and swinging heavy loads, great stress is imposed on the normal swing drive gears of such devices. This, of course leads to rapid wear of conventional swing drive pinions and ultimate failure, particularly where repeated swings are made under heavy load. While attempts have been made in the past to provide outboard, peripheral swing drive arrangements, these have not proved altogether satisfactory, due largely to eccentricities and other irregularities in the outer ring gear, leading to widely varying backlash on the driving pinion. Although, presumably this problem could be overcome by precision fabrication of the outer ring gear to insure concentricity of the ring and uniformity of teeth formation within close tolerances, even with todays' technology, this would be nearly prohibitively expensive.
According, it is the primary aim of the present invention to provide an improved swing drive assembly for heavy load handling devices which does not require machining large ring gear components to close tolerances.
It is a further object to provide such an improved swing drive assembly which is designed to provide substantially constant backlash on the swing drive pinion thus reducing stresses and prolonging swing gear life.
A more detailed object is to provide a swing drive assembly of the above type which includes means for maintaining the extent of tooth engagement between the driving pinion and the stationary ring gear uniform and constant regardless of eccentricities or other irregularities therein.
It is also an object of the invention to provide a swing drive assembly which may employ a large ring gear made up of a plurality of arcuate segments and/or a ring gear in which the teeth need not be precision machined, but instead may be formed by flame cutting, for example.
A still further detailed object of the invention is to provide an improved swing drive arrangement in which the force of maintaining a constant backlash on the swing drive pinion is imposed on the structure of the outer supporting roller path rather than being transmitted to the contral pivot of the rotating device.